Brit in Canada
Posts: 2
Joined: 7/13/2007
Status: offline
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1990 VW Jetta 1.8GL Automatic 4 Cylinder 8 Valve Gas Engine 280,000Km (175,000 Miles)
Digifant II ECU Fuel Injected
Recent relevant parts: Distributor Cap and Leads, Plugs, Air Filter, Injector Cleaner added to fuel.
At unpredictable moments the car will run very rich (over fueling) generally after having come to a stop and accelerating away. This can be with a hot or cold engine. The car hesitates will not accelerate and blows out a lot of black exhaust smoke. The performance improves after a few seconds especially if put into neutral and the engine reved. It will missfire and stutter but finally clear. When running normally the performance is good and when checked the spark plugs look as they should be - light grey/brown and clean. When running rich ALL 4 plugs are black and sooty. The tail pipe is also black and sooty.
Using the genuine Volkswagon Service Manual I have checked the Air Flow Sensor (moves freely and resistance varies proportionally to position) and the Intake Air Temperature Sensor. Both are good.
The Coolant Temperature Sensor is good.
The Exhaust Oxygen Sensor has 60,000Km (recommended to change every 100,000Km)
There is no blockage in the air intake system.
Any advice would be very welcome - Thanks, Roger
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Help please 1990 VW Jetta 1.8GL - 
